The present invention relates to automatic gain control (referred suitably to as xe2x80x9cAGCxe2x80x9d hereinafter) which is able to stabilize an input signal whose level is varied in a mobile communication device, etc. via gain control using a closed loop and then output it and, more particularly, an automatic gain control method and a device for embodying the same, which is able to execute the automatic gain control based on a transmission signal level (received signal strength indicator (RSSI) signal, etc.) detected from the input signal when a signal-to-noise (S/N) ratio of the input signal is degraded, and a radio communication device with such automatic gain control function.
In the prior art, in various signal processing devices, e.g., in the radio communication device, the automatic gain control (AGC) which stabilizes variation in a signal level of the received signal caused due to variation in a received electric field strength on a radio wave propagation path such as a radio line, etc. to reduce demodulation error, etc. is applied. As such automatic gain control, there are known the open loop control device in which a gain of a variable amplifier, etc. at the succeeding stage is controlled by an automatic gain control signal generated by detecting variation in the level of the input signal, and the close loop control device in which the gain of the variable amplifier, etc. at the preceding stage is controlled by the automatic gain control signal generated by detecting variation in the level of the input signal.
Under such automatic gain control, if the S/N of the input signal is degraded and thus a level of the input signal is reduced below a level of the noise signal, it becomes impossible to detect the variation in the level of the input signal. That is, it becomes impossible to generate an automatic gain control signal based on the input signal, so that the gain control of the variable amplifier at the preceding stage in the close loop control device cannot be carried out in answer to the variation of the input signal. In other words, if the device is employed under the noisy surroundings like the case the mobile telephone, the radio paging device (pager), or the like, for example, is employed with the movement under the surroundings with the extremely high noise level (surroundings in which there are much ignition noises of the vehicle, much radiation noises of electronic devices, etc.), or if the input signal level (received electric field strength) is low, the proper automatic gain control for the input signal cannot be achieved. In this case, there are such problems that good receiving characteristics cannot be assured and thus the received signal cannot be derived at a desired level.
As the digital AGC device, an example set forth in Patent Application Publication (KOKAI) Hei 9-83276 entitled xe2x80x9cAGC Amplifier Control Circuitxe2x80x9d is well known. In this example set forth in Patent Application Publication (KOKAI) Hei 9-83276, a gain obtained when the previous introduction of the input signal has been completed can be maintained at the time of starting the introduction of the input signal, so that this maintained gain is set in an AGC amplifier as an initial value and also the introduction error can be controlled by using a digital AGC loop. Accordingly, it is possible to delete the primary introduction of the input signal in an analogue format and thus to achieve high speed amplitude introduction control.
In the above-mentioned prior art, there is the problem that, when an S/N of the input signal is degraded and thus a level of the input signal is reduced below a level of the noise signal, reduction in a control voltage of a gain variable amplifier is caused and therefore proper automatic gain control cannot be achieved. That is, there is such a drawback that good receiving characteristics of the device cannot be achieved.
The present invention has been made to overcome such subject in the prior art, and it is an object of the present invention to provide an excellent automatic gain control method and a device for embodying the same, which is able to execute always proper automatic gain control and also achieve good receiving characteristics by preventing reduction in a control voltage of a gain variable amplifying means when an S/N of the input signal is degraded, and a radio communication device with such automatic gain control function.
In order to attain the above object, the automatic gain control method according to the first aspect of the present invention which achieves a constant output signal by controlling a gain variable amplifying means according to a control signal which is generated based on a level of an output signal which is derived by variably amplifying an input signal, comprises the steps of a output signal detecting step of detecting said output signal amplified by the gain variable amplifying means; a control signal generating step of generating the control signal for the gain variable amplifying means based on a detected output signal; a gain control state storing step of storing a gain control state every time when gain control of the gain variable amplifying means is executed; a input signal level detecting step of detecting a signal level from the input signal; a comparing step of comparing the input signal level with a control state set value which is defined previously; and a step of controlling a gain of the gain variable amplifying means by said control signal correspondence to the control state stored at preceding execution of the gain control when the signal level is reduced below the control state set value.
Preferably, the automatic gain control method according to the first aspect of the present invention which achieves a constant output signal by controlling a gain variable amplifying means according to a control signal which is generated based on a level of an output signal which is derived by variably amplifying an input signal, is characterized by comprising the steps of a detecting step of detecting an amplified output signal; a control signal generating step of generating the control signal for the gain variable amplifying means based on a detected voltage signal obtained by detection; a control signal storing step of storing the control signal every time when gain control of the gain variable amplifying means is executed; a signal level detecting step of detecting a transmitting signal level containing noises from the input signal; a comparing step of comparing the transmitting signal level with a threshold value which is defined previously; and a control signal outputting step of outputting the control signal stored at preceding execution of the gain control to the gain variable amplifying means when the transmitting signal level is reduced below the threshold value.
Also, the automatic gain control method according to the first aspect of the present invention which achieves a constant output signal by controlling a gain variable amplifying means according to a control signal which is generated based on a level of an output signal which is derived by variably amplifying an input signal, is characterized by comprising the steps of a detecting step of detecting an amplified output signal; a control signal generating step of generating the control signal for the gain variable amplifying means based on a detected voltage signal obtained by detection; a control signal holding step of holding the control signal; a signal level detecting step of detecting a transmitting signal level containing noises from the input signal; a signal level holding step of holding the transmitting signal level; a comparing step of comparing the transmitting signal level held at present execution of the gain control with the transmitting signal level held at preceding execution of the gain control; and a control signal outputting step of outputting the control signal held at preceding execution of the gain control to the gain variable amplifying means when the present control signal for a gain variable amplifier is lower in level than the preceding control signal for the gain variable amplifier and also the present transmitting signal level is reduced below the preceding transmitting signal level.
Also, the automatic gain control method according to the first aspect of the present invention which achieves a constant output signal by controlling a gain variable amplifying means according to a control signal which is generated based on a level of an output signal which is derived by variably amplifying an input signal, is characterized by comprising the steps of a detecting step of detecting an amplified output signal; a control signal generating step of generating the control signal for the gain variable amplifying means based on a detected voltage signal obtained by detection; a detected voltage signal holding step of holding the detected voltage signal; a signal level detecting step of detecting a transmitting signal level containing noises from the input signal; a signal level holding step of holding the transmitting signal level; a comparing step of comparing the transmitting signal level held at present execution of the gain control with the transmitting signal level held at preceding execution of the gain control; and a control signal outputting step of outputting the control signal to the gain variable amplifying means based on the detected voltage signal held at preceding execution of the gain control when the present control signal for a gain variable amplifier is lower in level than the preceding control signal for the gain variable amplifier and also the present transmitting signal level is reduced below the preceding transmitting signal level.
In order to attain the above object, the automatic gain control apparatus according to the second aspect of the present invention comprises a gain variable amplifying means which variably amplify an input signal in response to a control signal; an output signal detecting means which detects an output signal amplified by the gain variable amplifying means; a control signal generating means which generates the control signal for the gain variable amplifying means based on a detected output signal; a gain control state storing means which stores the gain control state every time when gain control of the gain variable amplifying means is executed; an input signal level detecting means which detects a signal level from the input signal; a comparing means which compares the signal level with the control state set value which is defined previously; and a controlling means which controls the gain of the gain variable amplifier means by the control signal corresponding to the control state stored at preceding execution of the gain control when the signal level is reduced below the control state set value.
Preferably, the automatic gain control device according to the second aspect of the present invention which achieves a constant output signal by controlling a gain variable amplifying means according to a control signal which is generated based on a level of an output signal which is derived by variably amplifying an input signal, is characterized by comprising a detecting means which detects an amplified output signal; a control signal generating means which generates the control signal for the gain variable amplifying means based on a detected voltage signal obtained by the detecting means; a control signal storing means which stores the control signal every time when gain control of the gain variable amplifying means is executed; a signal level detecting means which detects a transmitting signal level containing noises from the input signal; a comparing means which compares the transmitting signal level with a threshold value which is defined previously; and a control signal outputting means which outputs the control signal stored at preceding execution of the gain control to the gain variable amplifying means when the transmitting signal level is reduced below the threshold value.
Also, the automatic gain control device according to the second aspect of the present invention which achieves a constant output signal by controlling a gain variable amplifying means according to a control signal which is generated based on a level of an output signal which is derived by variably amplifying an input signal, is characterized by comprising a detecting means which detects an amplified output signal; a control signal generating means which generates the control signal for the gain variable amplifying means based on a detected voltage signal obtained by the detecting means; a control signal holding means which holds the control signal; a signal level detecting means which detects a transmitting signal level containing noises from the input signal; a signal level holding means which holds the transmitting signal level; a comparing means which compares the transmitting signal level held at present execution of the gain control with the transmitting signal level held by the signal level holding means at preceding execution of the gain control; and a control signal outputting means which outputs the control signal held by the control signal holding means at preceding execution of the gain control to the gain variable amplifying means when the present control signal for a gain variable amplifier is lower in level than the preceding control signal for the gain variable amplifier and the present transmitting signal level is reduced below the preceding transmitting signal level.
Also, the automatic gain control device according to the second aspect of the present invention which achieves a constant output signal by controlling a gain variable amplifying means according to a control signal which is generated based on a level of an output signal which is derived by variably amplifying an input signal, is characterized by comprising a detecting means which detects an amplified output signal; a control signal generating means which generates the control signal for the gain variable amplifying means based on a detected voltage signal obtained by the detecting means; a detected voltage signal holding means which holds the detected voltage signal; a signal level detecting means which detects a transmitting signal level containing noises from the input signal; a signal level holding means which holds the transmitting signal level; a comparing means which compares the transmitting signal level held at present execution of the gain control with the transmitting signal level held by the signal level holding means at preceding execution of the gain control; and a control signal outputting means which outputs the control signal to the gain variable amplifying means based on the detected voltage signal held by the detected voltage signal holding means at preceding execution of the gain control when the present control signal for a gain variable amplifier is lower in level than the preceding control signal for the gain variable amplifier and also the present transmitting signal level is reduced below the preceding transmitting signal level.
According to the present invention, it is provided a wireless communication device comprising a configuration of the automatic gain control device as mentioned above which is incorporated into a receiving system; and wherein automatic gain control for stabilizing an output signal associated with a receiving signal in the receiving system is carried out by the automatic gain control device.